Question

Using Clojure, how do I create the following object? The object is taken from java code (From Effective Java):

NutritionFacts cocaCola =
new NutritionFacts.Builder(240,8).calories(100).sodium(35).carbohydrate(27).build();

Answer 1

While it’s hard to argue with the concision in the other answers¹, .. has somewhat fallen out of favor, replaced by the more versatile ->. Personally I prefer :

(-> (NutritionFacts$Builder. 240 8) 
    (.calories 100)
    (.sodium 350)  
    (.carbohydrates 27) 
    (.build))

It’s a couple more characters, but you gain two things:

• Explicitness. I can look at the sodium line (for example) and tell it’s a Java method call, because the . is right there.
• Flexibility. If I need to, I can chain some non-method call in the middle there (printing it to stdout, say), or at the end of all this feed it in to some other function call.

Most importantly, every other answer to this question has gotten the classname wrong: Java’s NutritionFacts.Builder is language sugar over the real JVM class named NutritionFacts$Builder, and that class is the one Clojure must refer to (since we are not using javac to compile our code).

¹ I do disagree with the doto suggestion: it works only because this Builder class happens to implement its method-chaining by mutating a single instance and then returning it. doto is great for Java objects that require in-place mutation, but when a class is kind enough to pretend it’s immutable you should really be using the method-chaining version (ie, ->).